Many diverse observations suggest that extracellular, as well as intracellular, thiol-disulfide reactions are associated with cell growth control and that viral cell transfomation results in changes in such phenomena. A major hindrance to further investigation of the importance of such observations is the lack of a quantitative, sensitive, and specific analytical method for analysis of low molecular weight thiol-disulfide components. The specific aims of the present studies are: (1) to develop a general method for analysis of thiols, and thereby disulfide components, based upon isolation of thiols by affinity to a Sepharose-linked mercurial, conversion of the thiols to mixed disulfides of cystine, and quantitative measurement of the latter by conventional amino acid analysis; (2) to utilize this methodology to analyze the thiol, disulfide, and protein mixed disulfide content of two lines of normal cells (SV40-3T3 and MSV-MDCK), and simultaneously, of the growth media during exponential growth at low cell density and during growth at high cell density (confluent cells). The results of these studies will: (1) make available new methodology having widespread utility in basic research and clinical studies; (2) establish the low molecular weight thiol-disulfide composition of representative sera, normal mammalian cells, and virally transformed mammalian cells, and identify any previously unrecognized components; and, (3) establish in what way differences in thiol-disulfide content are associated with cell growth and viral cell transformation phenomena. The results could prove important in identifying new approaches to the detection and control of tumor cell growth.